﻿    <p>
      The <em>IfcRepresentation</em> defines the general concept of
      representing product properties and in particular the product
      shape.
    </p>
    <blockquote class="extDef">
      NOTE&nbsp; Definition from ISO 10303-43:<br>
      A representation is a collection of one or more representation items that are
      related in a specified representation context. The relationship of representation
			item to representation context is the basis for distinguishing which representation
			item entities are related.<br><br>
			A representation item can be related to a representation context directly, when it 
			occurs as an element is a representation, or indirectly, when it is referenced
			through any number of intervening entities, each of type representation item.
    </blockquote>
    <blockquote class="note">
      NOTE&nbsp; Entity adapted from
      <strong>representation</strong> defined in ISO 10303-42.
    </blockquote>
    <blockquote class="history">
      HISTORY&nbsp; New entity in IFC2.0
    </blockquote>
    <blockquote class="change-ifc2x3">
      IFC2x3 CHANGE&nbsp; The inverse attributes
      <em>LayerAssignments</em> and<em>RepresentationMap</em> have been
      added with upward compatibility.
    </blockquote>
    <blockquote class="change-ifc2x4">
      IFC4 CHANGE&nbsp; Entity <em>IfcRepresentation</em> has been
      changed into an ABSTRACT supertype.
    </blockquote>
    <p class="use-head">
      Representation Use Definition
    </p>
    <p>
      Each representation, either <em>IfcShapeRepresentation</em>, or
      <em>IfcTopologyRepresentation</em> shall have a well defined:
    </p>
    <ul>
      <li>
        <em>ContextOfItems</em>: Reference to an
        <em>IfcGeometricRepresentationContext</em> as agreed for this
        representation.
      </li>
      <li>
        <em>RepresentationIdentifier</em>: Name of the
        representation, for example, 'Body' for 3D shape,
        'FootPrint' for 2D ground view, 'Axis' for reference axis.
      </li>
      <li>
        <em>RepresentationType</em>: Name for the geometric, or
        topological representation type, for example, 'SweptSolid'
        for 3D swept solids, 'Brep' for boundary representation.
      </li>
    </ul>
    <blockquote class="note">
      NOTE&nbsp; Guidelines for applying correct values to those
      attributes are provided in the geometry use definition
      section at each subtype of <em>IfcElement</em>. These
      guidelines can be further refined in view definitions or
      implementer agreements.
    </blockquote>